In recent years, deep convolutional neural networks (CNNs) have shown
promise for improving prostate cancer diagnosis by enabling quantitative
histopathology through digital pathology. However, there are a number of
factors that limit the widespread adoption and clinical utility of deep learning
for digital pathology. One of these limitations is the requirement for large
labelled training datasets which are expensive to construct due to limited availability
of the requisite expertise. Additionally, digital pathology applications
typically require the digitisation of histological slides at high magnifications.
This process can be challenging especially when digitising large histological
slides such as prostatectomies.
This work studies and addresses these issues in two important applications
of digital pathology: prostate nuclei detection and cell type classification. We
study the performance of CNNs at different magnifications and demonstrate
that it is possible to perform nuclei detection in low magnification prostate
histopathology using CNNs with minimal loss in accuracy. We then study the
training of prostate nuclei detectors in the small data setting and demonstrate
that although it is possible to train nuclei detectors with minimal data, the
models will be sensitive to hyperparameter choice and therefore may not generalise
well. Instead, we show that pre-training the CNNs with colon histology
data makes them more robust to hyperparameter choice.
We then study the CNN performance for prostate cell type classification
using supervised, transfer and semi-supervised learning in the small data setting.
Our results show that transfer learning can be detrimental to performance but semi-supervised learning is able to provide significant improvements to the
learning curve, allowing the training of neural networks with modest amounts
of labelled data. We then propose a novel semi-supervised learning method
called Deeply-supervised Exemplar CNNs and demonstrate their ability to improve
the cell type classifier learning curves at a much better rate than previous
semi-supervised neural network methods
